Serum uric acid, phosphorus and glucose concentrations were determined using commercially available kits (Labtest Diagnóstica SA, Lagoa Santa, Minas Gerais, Brazil) in an automated multi-biochemical analyzer (Cobas Miras Plus, Roche®, Germany). Serum potassium levels were measured in an automated Dimension Max System (Siemens Healthcare Diagnostics Products®, Germany), according to the manufacturer's instructions.